Sonoluminescence from Aqueous Alcohol and Surfactant Solutions

Abstract

The sonoluminescence generated in water with pulsed 515 kHz ultrasound has been studied in the presence of different chain length (C1−C5) aliphatic alcohols and the surfactants sodium dodecyl sulfate (SDS), dodecyltrimethylammonium chloride (DTAC), and N-dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (DAPS). The ultrasound pulse widths used ranged from 1 to 10 ms, with duty cycles (on/off ratios) of 1:3 to 1:9. It was found that the sonoluminescence from the initial pulses was very low but increased in intensity and reached a maximum after 20−50 pulses, for all systems studied, depending on the pulse width and duty cycle. In the presence of alcohol the maximum signal decreased with increasing alcohol concentration, and the signal decline was more pronounced with increasing chain length of the alcohol. A good correlation was found to exist between the decline in the sonoluminescence signal and the Gibbs surface excess of the alcohol at the air/water interface. In the presence of SDS (an anionic surfactant) and DTAC (a cationic surfactant), quite different behavior was observed. At low concentrations of these two surfactants the maximum signal was significantly enhanced over that obtained in pure water, reaching a maximum at about 1 mM of surfactant. At higher concentrations the signal decreased again reaching a limiting value similar to that obtained in pure water. The sonoluminescence signal in DAPS (a zwitterionic surfactant) solutions remained much the same as in pure water. On the addition of 0.1 M NaCl to the three different types of surfactant solutions, the intensities of the emission signals obtained were essentially the same as in pure water. Possible mechanisms responsible for the different behavior in the sonoluminescence signal in the presence of the alcohols and surfactants are discussed.

A parametric review of sonochemistry: Control and augmentation of sonochemical activity in aqueous solutions

“…The resistance to mass transfer has been shown to be surfactant concentration dependant; 10 mM as opposed to 1 mM of DTAC presents an increase in resistance [141]. It has been found that as the alkyl chain length of the surfactant increases the amount of solute able to be adsorbed at the surface decreases [231]. Therefore the degree to which the surfactant is able to be adsorbed at the surface of the bubble presents a limiting factor rather than the concentration of solute in the solution [215].…”

“…It was suggested that by using a highly charged surfactant bubbles would not be able to reach minimum size due to repulsions at the surface, however this was not apparent during experimentation [229]. Alcohols (especially with a terminal hydroxyl group) act in a similar vein to SDS with their nonpolar and polar surface properties reducing coalescence and increasing the number of active bubbles [31,47,231]. Tronson et al found that water solutions containing certain aliphatic alcohols quenched sonoluminescence at 515 kHz but indicated that by choosing the correct frequency it would be possible to increase sonochemical reactions [48].…”

“…For example, when molecules are changed to their more volatile version using pH, they are evaporated into the bubble and are able to quench sonoluminescence. However, in the ionic form, the molecules remained in the solution and did not quench sonoluminescence, although they were still subject to radical degradation reactions [64,215,231]. Thus, pH may influence chemical dynamics of the system such that it may act to control the reactions taking place.…”

Sonochemical removal of naphthol blue black azo dye: influence of parameters and effect of mineral ions

“…Finally, non-volatile and hydrophobic molecule will undergo mainly radical attacks at the cavitation bubble interface (Ashokkumar et al 1997Barbour et al 1999).…”

Size Distribution of Cavitation Bubbles

“…The modifications to the instrument allowed the delivery of pulsed ultrasound with a variable pulse-on time between 0.1 and 25 ms and pulse-off time between 0.8 ms and 6 s. The reactor was placed in a light-shielded housing, which also contained an end-on photomultiplier (Hamamatsu) for recording the SL from the insonated solutions (Ashokkumar et al 1997).…”